In communication devices such as battery powered two way portable radios, there is a great need for power amplifiers which exhibit high operating efficiencies, and low current drain characteristics. This is due to the limited amount of battery capacity available in portable radios, combined with the increasing demands by radio users to operate radios for longer periods of time without recharging the batteries. Since the power amplifiers used in radios are one of the key current consuming devices of a radio, there is always a need for higher efficiency amplifiers in radio designs. Unfortunately, power amplifiers which exhibit high efficiencies such as "Class B" amplifiers, tend to have problems with what is known as frequency splatter, due to the fact that a Class B amplifier will turn on very quickly (as soon as an input signal to the amplifier is applied which is high enough to bias the amplifier). This high speed turn on and off operation of the amplifier causes frequency harmonics to be transmitted which are undesired. Unwanted harmonics are especially a problem in time division multiplexing (TDM) communication equipment due to the high rate of operation of the transmitter, which contributes to greater harmonic problems. Frequency splatter not only causes interference with the transmitted signal, but also causes problems in meeting regulatory agency requirements (e.g. FCC, etc.) that most countries impose on communication equipment.
A need for a high efficiency amplifier circuit which can attain high efficiencies, as well as exhibit minimal frequency splatter would be very useful for use in communication equipment, and would be especially useful in TDM applications. A bias circuit which could take the high efficiency amplifier characteristics of a Class B amplifier or other high efficiency amplifier class, and give it the low splatter characteristics of a class A amplifier (or other similar low splatter class) would be very beneficial in minimizing the problems associated with frequency splatter.